The U.S. economy added a net 74,000 jobs in the last month of 2013, based on preliminary figures. That’s the smallest rise in three years and a big stumble from November’s outsized 241,000 gain. Economists had projected a much larger 193,000 advance for December. Read full report on lackluster jobs increase.

A midmonth cold snap made the December report weaker, Wall Street economists say. Bad weather may have reduced the reported number of new jobs by 50,000 to 100,000.

One clue is the spike in the number of people who said they could not work because of bad weather. It surged to 273,000 from a longer-term average of 166,000. That’s also the highest amount for the month of December since 1977, points out Neil Dutta, head of economics at Macro Renaissance Research.

What’s odd is that hardly anybody on Wall Street factored poor weather into their forecasts even though the topic was much discussed. One of the few who made the correct call was Robert DiClemente, chief U.S. economist at Citigroup Global Markets. And he expects January to offer another challenge because of the polar vortex that put half the country in a deep freeze.

Whatever the case, the huge swing between November and December doesn’t mean companies suddenly took a Jekyll-and-Hyde approach to hiring . The schizophrenic jobs data more likely reflected the trouble faced by government economists in adjusting for seasonal variations around the holiday season when the weather is poor.

“It’s not that actual hiring is volatile,” DiClemente said. “It’s just our ability to track employment.”

That’s not to say the December report should be ignored as many investors appear to have done. The details imply the economy is not as strong as suggested by the employment gains in November – a report extolled at the time by bulls on Wall Street and in Washington.

“One can neither put a positive spin on the December employment report nor, if having celebrated the strong reports of recent months, ignore it,” said Richard Moody, chief economist at Regions Financial in Alabama. He’s inclined to discount the report but also said it “can’t help but to bring some doubts into our minds.”

A better way to look at job growth in the waning months of 2013 is to check the monthly average in the fourth quarter – 172,000. That’s just slightly below the annual average of 182,000.

The upshot: The economy is still expanding at a moderate clip, with the chance for speedier growth later in 2014.